310 THE ACTION OF NATURAL 



the selected portion of each succeeding generation will 

 therefore be stronger, swifter, and more thickly furred 

 than the last ; and if this process goes on for thousands 

 of generations, our animal will have again become 

 thoroughly in harmony with the new conditions in 

 which it is placed. But it will now be a different 

 creature. It will be not only swifter and stronger, 

 and more furry, it will also probably have changed in 

 colour, in form, perhaps have acquired a longer tail, 

 or differently shaped ears ; for it is an ascertained 

 fact, that when one part of an animal is modified, 

 some other parts almost always change, as it were in 

 sympathy with it. Mr. Darwin calls this " correlation 

 of growth," and gives as instances, that hairless dogs 

 have imperfect teeth ; white cats, w r hen blue-eyed, are 

 deaf; small feet accompany short beaks in pigeons ; 

 and other equally interesting cases. 



Grant, therefore, the premises : 1st. That peculiari- 

 ties of every kind are more or less hereditary. 2nd. 

 That the offspring of every animal vary more or less 

 in all parts of their organization. 3rd. That the 

 universe in which these animals live, is not absolutely 

 invariable ; none of which propositions can be denied ; 

 and then consider, that the animals in any country 

 (those at least which are not dying out) must at each 

 successive period be brought into harmony with the 

 surrounding conditions ; and we have all the elements 

 for a change of form and structure in the animals, 

 keeping exact pace with changes of whatever nature 

 in the surrounding universe. Such changes must be 



